Health insurance industry trade groups opposed to President Obama's health care reform bill are paying Facebook users fake money -- called "virtual currency" -- to send letters to Congress protesting the bill.

Here's how it's happening:

Facebook users play a social game, like "FarmVille" or "Friends For Sale." They get addicted to it. Eager to accelerate their progress inside the game, the gamers buy "virtual goods" such as a machine gun for "Mafia Wars." But these gamers don't buy these virtual goods with real money. They use virtual currency.

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